As handheld and portable electronic devices (e.g., smartphones, tablets, wearables, etc.) increase in capability and functionality, the electronic components within the devices must provide improved computational performance levels. In order to achieve the higher computational performance levels, electronic devices tend to dissipate increasing amounts of energy in the form of heat. Due to the compact size associated with typical portable electronic devices, the energy dissipation can result in temperature increases both within the electronic device and at the exterior surface (or “skin”) associated with the device. Accordingly, because human skin can be sensitive to the heat dissipated at the device surface, the skin or surface temperature is a critical design constraint in many (if not all) electronic devices that are designed to come into contact with the human body (e.g., a user's hand, ear, face, etc.). For example, temperatures at one or more device surfaces (e.g., a housing surface, a back cover surface, a liquid crystal display (LCD) surface, etc.) may become too hot to touch, thus leading to an uncomfortable user experience. Furthermore, high temperature surfaces can become a safety hazard due to local skin burning. Accordingly, performance in handheld and other portable electronic devices tends to be limited due to limited power budgets based on thermal limits on skin temperature and silicon junction temperature (Tj), wherein the latter refers to the temperature limit on active layers in the semiconductor chip or chips within the device. However, skin temperature tends to be the more strict limits and represents the performance bottleneck in most use cases.
One issue that engineers and designers face when attempting to adhere to the above-mentioned thermal limitations is the difficulty to directly measure the skin temperature. For example, portable electronic devices typically do not have sufficient space to house active cooling devices, such as fans, which are often found in larger computing devices such as laptop and desktop computers. Instead, portable electronic devices may be designed to spatially arrange electronic components so that two or more active and heat-producing components are not positioned proximally to one another. Many portable electronic devices also rely on passive cooling devices, such as heat sinks, to manage thermal energy among the heat-producing electronic components. However, due to size limitations, portable electronic devices typically do not have enough space to use clever spatial arrangements or strategically placed passive cooling components. Therefore, current systems and methods typically employ on-chip and/or on-board temperature sensors to predict skin temperature based on calibration tests. In reality, however, predicting skin temperature using on-chip and/or on-board temperature sensors may be inaccurate because the on-chip and/or on-board temperature sensors may be sensitive to power changes (e.g., due to active usage) even though skin temperature may respond more slowly. Furthermore, in other situations, the on-chip and/or on-board temperature sensors may not react to increases in skin temperature that occur independently from on-chip and/or on-board activity (e.g., where the battery becomes hot while charging despite the device not being in active use).